In hydraulic compositions such as concrete compositions, water-soluble cellulose ethers are used for imparting material segregation resistance, bleeding reduction effect, and fluidity thereto. The hydraulic composition to which a water-soluble cellulose ether is added, however, may have an excessive air content because the water-soluble cellulose ether has a surface-active effect to entrain more air bubbles during mixing of the hydraulic composition. The air bubbles entrained with the aid of the water-soluble cellulose ether have a large diameter outside the effective range for frost damage resistance. It is thus a common practice to use a defoamer to remove coarse air bubbles.
For imparting frost damage resistance to the hydraulic composition, fine air bubbles having a diameter of about 25 to about 250 μm must be entrained into the hydraulic composition. To this end, air entraining (AE) agents are typically used. In the case of a hydraulic composition having a water-soluble cellulose ether added thereto, a defoamer must be used as mentioned above for the purpose of eliminating air bubbles entrained due to the water-soluble cellulose ether, thereby achieving the desired air content. This composition is difficult to satisfy frost damage resistance because the defoamer eliminates not only air bubbles entrained by the water-soluble cellulose ether, but also fine air bubbles entrained by the AE agent.
To solve the problem, for example, Patent Document 1 proposes to use O-2,3-dihydroxypropyl cellulose (DHPC) having a low air entraining ability, as the water-soluble cellulose ether. Patent Document 2 proposes to use hollow microbeads instead of the AE agent. Patent Document 3 discloses an AE agent which is effective for use in a cement composition containing fly ash.